This project examines the role of fibronectin (Fn) in regulating epithelial invasion of the extracellular matrix (ECM) during airway submucosal gland (SMG) morphogenesis. Interest in specific, alternatively-spliced isoforms of the glycoprotein fibronectin as mediators of epithelial morphogenesis is supported by the developmental biology literature and preliminary data from our laboratory using cultured human cells which morphologically model early SMG development. Using immuno-histochemistry and in situ hybridization, active Fn isoforms will be localized in our cell culture model and neonatal rat SMGs in vivo. Transcriptional and translational regulation of specific Fn isoform expression in various human cell lines will be investigated by nuclease protection assay and immunoblotting. This will be correlated with the cell lines' ability to promote epithelial ECM invasion in vitro. Finally, cell lines constitutively unable to support epithelial invasion will be transfected with cDNA constructs from Fn domains specific for the isoforms identified as important to epithelial invasion. Transfected fibroblasts will be compared to untransfected controls to determine if expression of these sequences confers the ability to promote epithelial invasive behavior in vitro. These studies may have relevance beyond airway development for clinical problems such as repair after injury and tumor progression.